I Need Help For My Server

This Is The Error I have

CONSOLE

Exception in thread "main" java.lang.UnsupportedClassVersionError: net/md_5/bungee/api/ProxyServer : Unsupported major.minor version 51.0

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClassCond(ClassLoader.java:637)

at java.lang.ClassLoader.defineClass(ClassLoader.java:621)

at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)

at...

I Need Help For My Server